A magnetic disk drive comprises a disk (more specifically a magnetic disk) as a recording medium. Now, it is assumed that a fine projection (hereinafter referred to as a media bump) is present on a disk. This may preclude a head (more specifically a magnetic head) from writing or reading data to or from an area on the disk in which the media bump is present. Furthermore, the head may collide against the media bump and be degraded (or damaged). To avoid such a phenomenon (particularly the collision between the head and the media bump), various methods for detecting a defect such as a media bump which is present on the disk (more specifically a recording surface of the disk) have been proposed.
A known method for detecting a defect on the disk uses an HDI sensor. Like a write element and a read element, the HDI sensor is generally mounted in a head (more specifically, a head slider) for use. The HDI sensor electrically detects interference acting between the head and the disk (that is, interaction), for example, thermal interference. When the HDI sensor detects thermal interference that exceeds a threshold, a location on the disk (for example, a cylinder position) where the read element is positioned is detected as the location of a defect. The defect detection method using the HDI sensor is suitable for detection of a defect such as a media bump against which the head may collide. The defect detection using the HDI sensor is executed by scanning the disk using the head.
For each of all defects detected by the HDI sensor, a controller in the magnetic disk drive determines an area on the disk including a location at which the defect has been detected and the periphery of the location to be a defect area on which a write/read operation should be avoided (hereinafter referred to as a track slip area). Information indicative of the track slip area is recorded in a table (hereinafter referred to as a track slip management table). The controller identifies the track slip area on the disk on which no write/read operation is to be performed based on the track slip management table. The controller avoids writing and reading data to and from the identified track slip area. That is, the controller avoids moving the head to the cylinder area (range) on the disk in which the identified track slip area is present.
However, the location detected as a defect using the HDI sensor is where the read element is positioned at the time of the detection as described above. That is, the location detected as a defect using the HDI sensor is different from a location where the HDI sensor is located at the time of the detection. Thus, when a track slip area is determined without taking this shift of the detected position into account, it is difficult to avoid a possible collision of the head against a media bump during a write/read operation.
On the other hand, when the track slip area is extended in an inner direction and an outer direction of the disk with the shift of the detected position taken into account, a possible collision of the head against a media bump during a write/read operation can be avoided, thereby preventing the head from being degraded. However, when the shift of the detected position is taken into account, the track slip area is extended more than necessary. In this case, locations available as data areas decrease, thereby making a storage capacity needed for the magnetic disk drive difficult to achieve.
The amount of shift of the detected position varies depending on the radial position of the head on the disk. This is because the head moves in the radial direction of the disk so as to draw an arc. That is, the amount of shift varies depending on the yaw angle θ of the head. Thus, the amount by which the track slip area is extended is expected to be varied depending on the yaw angle θ of the head. Even in this case, a track slip area with a large yaw angle θ is extended more than necessary, thereby reducing the locations available as data areas.